InfoSec Handlers Diary Blog

Microsoft introduced the ability to block file formats to the different programs in office and safer ways to open suspect files about a year ago.

The file blocking is not based on the file extension but on the actual format (so renaming a rich text file (.rtf) to a .doc won't get around the restriction). Unfortunately it's set by making changes in the registry and perhaps worse: it's a blacklist instead of a list of allowed file types. Still if you never intend to open e.g. rtf files, you could block it.

Microsoft Office Isolated Conversion Environment (MOICE) is an alternate way to open office files away from the actual tool. Use it instead of the real thing if you cannot resist opening that unsolicited attachment promising whatever it promises.

We will update issues on this page as they evolve.We appreciate updates
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(*): ISC rating

We use 4 levels:

PATCH NOW: Typically used where we see immediate danger of exploitation. Typical environments will want to deploy these patches ASAP. Workarounds are typically not accepted by users or are not possible. This rating is often used when typical deployments make it vulnerable and exploits are being used or easy to obtain or make.

Critical: Anything that needs little to become "interesting" for the dark side. Best approach is to test and deploy ASAP. Workarounds can give more time to test.

Important: Things where more testing and other measures can help.

Less Urgent: Typically we expect the impact if left unpatched to be not that big a deal in the short term. Do not forget them however.

The difference between the client and server rating is based on how you use the affected machine. We take into account the typical client and server deployment in the usage of the machine and the common measures people typically have in place already. Measures we presume are simple best practices for servers such as not using outlook, MSIE, word etc. to do traditional office or leisure work.

The rating is not a risk analysis as such. It is a rating of importance of the vulnerability and the perceived or even predicted threat for affected systems. The rating does not account for the number of affected systems there are. It is for an affected system in a typical worst-case role.

Only the organization itself is in a position to do a full risk analysis involving the presence (or lack of) affected systems, the actually implemented measures, the impact on their operation and the value of the assets involved.

All patches released by a vendor are important enough to have a close look if you use the affected systems. There is little incentive for vendors to publicize patches that do not have some form of risk to them.

Debian and Ubuntu Linux users should look into their OpenSSH setup. It turns out the PRNG (Pseudo Random Number Generator) as used was predictable.

Remember patching isn't enough, you need to regenerate keys generated on these machines! Including those used in SSL certificates (X.509).

Worse: even good keys apparently can be exposed due to this. Quoting from the Debian reference below:

"Furthermore, all DSA keys ever used on affected Debian systems for signing or authentication purposes should be considered compromised; the Digital Signature Algorithm relies on a secret random value used during signature generation."

So merely using your (good) keys on an affected machine might be enough to get the key itself compromised.